CN113731195B - Synthesis method and application of mixed metal organic framework film - Google Patents

Abstract

The invention belongs to the field of novel functional materials, and discloses a synthesis method and application of a mixed metal organic framework film. The design idea of the synthesis method of the invention is as follows: firstly synthesizing metal organic framework particles, then uniformly dispersing the metal organic framework particles in the multifunctional metal gel, and forming the mixed metal organic framework film after heating treatment. According to the invention, the MOF film is used as a continuous phase matrix, and the MOF particles with higher specific surface area or larger aperture are doped to be used as a disperse phase, so that the novel mixed metal organic framework matrix film is constructed. The addition of metal organic framework particles not only can increase the permeation flux and selectivity of the MOF membrane, but also can provide more heterogeneous nucleation sites for the growth of the membrane and promote the continuity of the membrane. Therefore, the method can be well applied to gas separation and purification.

Description

Synthesis method and application of mixed metal-organic framework membrane

Technical field

The invention belongs to the field of new functional materials, and particularly relates to a synthesis method and application of a mixed metal-organic framework membrane.

Background technique

Membrane separation has attracted great interest in purification and separation due to its environmental friendliness, process convenience, and low energy consumption. As the earliest separation membrane developed, polymer membranes have the advantages of being cheap, easy to process, and easy to load. Polymer membranes are usually made from organic polymers. However, traditional polymer membranes suffer from the "Robertson upper limit" between selectivity and permeability and cannot achieve high flux and high selectivity simultaneously, which hinders their further application. In order to improve the separation performance of polymer membranes, porous materials, such as zeolite molecular sieves and covalent organic framework materials, are added to the polymer matrix to construct mixed matrix membranes (MMMs). Among many nanoporous materials, metal-organic frameworks (MOFs) have attracted widespread attention due to their highly diverse structures, regular pores, and functionalizability. However, the performance of MMMs is greatly limited by polymer properties. In general, the loading of fillers in MMMs is usually limited to less than 40 wt%. Excessive loading will cause particle agglomeration and sedimentation, thereby reducing the separation performance of the membrane.

Compared with mixed matrix membranes, MOFs have better compatibility with each other and can build particle-penetrated membranes to avoid the formation of phase interface defects. At the same time, MOF membranes exhibit higher permeation fluxes. According to the different precursor phases, the methods for constructing conventional MOF films can be divided into two categories, including solution method and vapor deposition method. The solution method usually immerses the porous substrate into a precursor mixture or interface through heterogeneous crystallization to assemble into a continuous MOF layer. The vapor deposition method mainly constructs continuous MOF films through vapor deposition reactions of metal precursors and organic ligands. It is difficult for the solution method to add nano/micron particles before film formation and form a composite layer with excellent dispersion, as in the preparation of MMMs; at the same time, this method involves problems such as homogeneous/heterogeneous crystallization competition and large solvent consumption. The vapor deposition method also involves the regular assembly of molecules and cannot be easily used to construct hybrid metal-organic framework membranes. Therefore, the current preparation method of metal-organic framework membranes cannot simultaneously obtain a continuous MOF membrane and introduce heterogeneous MOF particles to improve the separation performance of the membrane. Therefore, exploring and developing a new synthesis method for hybrid metal-organic framework membranes is of great significance for the industrial preparation and practical application of metal-organic framework membranes.

Contents of the invention

In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, the primary purpose of the present invention is to provide a synthesis method of a mixed metal-organic framework membrane. The design idea of the synthesis method of the present invention is: first synthesize metal-organic framework particles, and then uniformly disperse the metal-organic framework particles in the multifunctional metal gel. After heat treatment, a mixed metal-organic framework film is formed. The addition of metal organic framework particles can not only provide more heterogeneous nucleation sites for the growth of metal organic framework films, but also provide transport channels for gas molecules.

Another object of the present invention is to provide a mixed metal organic framework membrane synthesized by the above method.

Another object of the present invention is to provide the application of the above-mentioned mixed metal organic framework membrane.

The object of the present invention is achieved through the following solutions:

A method for synthesizing mixed metal-organic framework membranes, including the following steps:

(1) Preparation of metal-organic framework particles: Add metal salt A and organic ligand A to solvent A, mix evenly to obtain a synthetic solution, subject the synthetic solution to a solvothermal reaction, and after the reaction is completed, wait for it to cool naturally before washing and drying. , obtain metal-organic framework particles;

(2) Prepare mixed metal gel: Add metal salt B to solvent B, stir and disperse evenly at 30 to 80°C, then add chelating agent, continue the constant temperature stirring reaction for 10 to 80 minutes to obtain a metal sol, and mix the metal organic framework particles Add to the obtained metal sol, mix evenly and cool to room temperature, then add organic ligand B and stir evenly to obtain a mixed metal gel containing metal-organic framework particles;

(3) Synthesis of mixed metal-organic framework membrane: Coat the mixed metal gel containing metal-organic framework particles obtained in step (2) on the substrate, then heat-treat at 60-250°C for 12-48 hours, and then naturally cool to room temperature. , take out the synthesized membrane, soak it in solvent C and dry it to obtain the mixed metal-organic framework membrane.

The metal element in the metal salt A described in step (1) is one of Zn, Al, Fe, Cu, Ti, Cr, Co, Ni, Mg, Zr, Nb, Mo, Mn, Sm, and Gd; The metal salt A is usually a metal nitrate, chloride, carbonate, sulfate or acetate, specifically zinc nitrate, cobalt nitrate, zinc acetate, copper chloride, zinc chloride, aluminum chloride, One of copper nitrate and zirconium chloride.

The organic ligand A described in step (1) is 2-imidazolecarboxaldehyde, 2-methylimidazole, 4-bromoimidazole, imidazole, benzimidazole, terephthalic acid, trimesic acid, 2-amino One of terephthalic acid and 1,4-phthalic acid;

The ratio of the amounts of metal salt A and organic ligand A described in step (1) is 1:0.5-8 (preferably 1:1-2);

Solvent A described in step (1) is one of solvent D, a mixture of solvent D and water, or a mixture of hydrofluoric acid and water, wherein solvent D is methanol, N, N-dimethylacetamide, At least one of N,N-diethylformamide, N,N-dimethylformamide, octanol, and ethanol; the solvent A is only used as a reaction medium and does not participate in the reaction, so there is no need to limit Usage amount: Preferably, 4000 to 110000 mL of solvent A is used for every 1 mol of metal salt A, and more preferably, 6000 to 50000 mL of solvent A is used;

The solvothermal reaction described in step (1) refers to heat treatment in a stainless steel autoclave lined with polytetrafluoroethylene at 40 to 300°C for 6 to 72 hours.

The washing described in step (1) is preferably carried out with at least one of solvent D, a mixture of solvent D and water, and a mixture of hydrofluoric acid and water, wherein solvent D is methanol, N, N-dihydrogen. At least one of methylacetamide, N,N-diethylformamide, N,N-dimethylformamide, octanol, and ethanol.

The metal element in the metal salt B described in step (2) is one of Zn, Al, Fe, Cu, Ti, Cr, Co, Ni, Mg, Zr, Nb, Mo, Mn, Sm, and Gd; The metal salt B is usually a metal nitrate, chloride, carbonate, sulfate or acetate, specifically zinc nitrate, cobalt nitrate, zinc acetate, copper chloride, zinc chloride, aluminum chloride, One of copper nitrate and zirconium chloride.

Solvent B described in step (2) is a monohydric alcohol, a glycol and derivatives of alcohols, preferably ethanol, propanol, butanol, ethylene glycol, propylene glycol, glycerin, ethylene glycol ether or ethyl glycol. One of the glycol methyl ethers; the volumetric dosage of the solvent B is 0.5 to 50 mL/g (preferably 2 to 22 mL/g) based on the mass of the metal salt B.

The chelating agent described in step (2) is one of ethanolamine, ethylenediamine, diethanolamine, triethanolamine, 2-aminoethanol, triethylamine, diethylenetriamine or ammonia, preferably ethylenediamine, ethanolamine Or one in ammonia water; the ratio of the amount of the chelating agent to the metal salt B is 1:0.5~8 (preferably 1:1~3);

The organic ligand B in step (2) is at least one of 2-imidazolecarboxaldehyde, 2-methylimidazole, 4-bromoimidazole, imidazole, benzimidazole, terephthalic acid and trimesic acid; The ratio of the amounts of the metal salt B and the organic ligand B is 1:0.5-12 (preferably 1:1-5).

The metal organic framework particles described in step (2) are at least one of the metal organic framework particles prepared in step (1).

The ratio of the amount of the metal organic framework particles described in step (2) to the mass of the metal organic framework material generated by the metal gel is 0 to 50% (preferably 0 to 20%).

The configuration of the substrate described in step (3) is a flat plate, a tube or a hollow fiber type; the material of the substrate described in step (3) is polypropylene, polyethylene, alumina, titanium dioxide, copper, polytetraethylene. Vinyl fluoride, polyimide, polyetheretherketone, polyvinylidene fluoride, polyacrylonitrile, polysulfone, polyethersulfone, cellulose or zinc, preferably polysulfone, polyethersulfone, anodized aluminum, polyacrylonitrile , polyvinylidene fluoride, polyetherimide or polyacrylonitrile.

In step (3), the solvent C is methanol, N,N-dimethylacetamide, N,N-diethylformamide, N,N-dimethylformamide, octanol, and ethanol. At least one.

A mixed metal organic framework membrane prepared by the above method.

Application of the above-mentioned mixed metal organic framework membrane in gas separation and purification.

Compared with the existing technology, the present invention has the following advantages and beneficial effects:

(1) Using the MOF membrane as the continuous phase matrix and doping MOF particles with higher specific surface area or larger pore size as the dispersed phase, a new type of mixed metal-organic framework matrix membrane is constructed.

(2) The addition of metal-organic framework particles can not only increase the permeation flux and selectivity of the MOF membrane, but also provide more heterogeneous nucleation sites for membrane growth and promote membrane continuity.

(3) The method of the present invention has broad versatility and can be applied to the construction of a variety of mixed metal-organic framework membranes, and has good application value and prospects.

Description of the drawings

Figure 1 is an SEM image of the UiO-66-NH ₂ mixed ZIF-8 matrix membrane prepared in Example 1 of the present invention. In the figure, (a) is the membrane surface and (b) is the cross section;

Figure 2 is the XRD pattern of UiO-66-NH ₂ mixed ZIF-8 matrix membrane prepared in Example 1, UiO-66-NH ₂ and ZIF-8 prepared in Comparative Example; wherein ZIF-8 represents the ZIF-8 prepared in Comparative Example 1 ZIF-8 membrane, U _N ZM ₅ represents UiO-66-NH ₂ mixed ZIF-8 matrix membrane;

Figure 3 is a gas flux comparison diagram of the UiO-66-NH ₂ mixed ZIF-8 matrix membrane prepared in Example 1 of the present invention and the ZIF-8 membrane prepared in the comparative example. Among them, ZIF-8 represents the flux of the ZIF-8 membrane prepared in Comparative Example 1, and U _N ZM ₅ represents the flux of the UiO-66-NH ₂ mixed ZIF-8 matrix membrane;

Figure 4 is an SEM image of the MIL-101 mixed ZIF-8 matrix membrane prepared in Example 2 of the present invention. In the figure, (a) is the membrane surface and (b) is the cross section;

Figure 5 is an SEM image of the UiO-66 mixed ZIF-8 matrix membrane prepared in Example 3 of the present invention. In the figure, (a) is the membrane surface and (b) is the cross section;

Figure 6 is an SEM image of the ZIF-8 membrane prepared in the comparative example of the present invention. In the figure, (a) is the membrane surface and (b) is the cross section.

Detailed ways

The present invention will be described in further detail below with reference to the examples and drawings, but the implementation of the present invention is not limited thereto. If the specific conditions are not specified in the examples, the conditions should be carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not indicated, they are all conventional products that can be purchased commercially.

In the present invention, the terms "metal salt A" and "metal salt B" have no special meaning. They all refer to metal salts in the general sense. The marks "A" and "B" are only used to distinguish the metals used in different steps. Salt. The terms "organic ligand A", "organic ligand B", "solvent A", "solvent B", "solvent C" and "solvent D" are the same.

The reagents used in the examples can all be purchased from the market unless otherwise specified.

Example 1

The MOF particles are UiO-66-NH ₂ , the metal gel is zinc gel, the substrate is an anodized aluminum substrate (AAO), and the synthesized mixed metal-organic framework film is a UiO-66-NH ₂ mixed ZIF-8 matrix film.

Preparation:

(1) Preparation of UiO-66-NH ₂ : UiO-66-NH ₂ is prepared by solvothermal synthesis method. Zirconium chloride (0.48 g) and 2-aminoterephthalic acid (0.372 g) were dissolved in N,N-dimethylformamide (40 mL) and water (0.19 mL) by stirring and sonication. The solution was transferred to a Teflon-lined stainless steel autoclave and heat treated at 120 °C for 24 h. After natural cooling, the powder was separated by centrifugation at 6000 rpm for 5 min. Finally, the obtained powder was washed several times with N,N-dimethylformamide and methanol.

(2) Prepare gel containing UiO-66- _NH2 : Add zinc acetate (3.467g) to ethanol (10mL), stir at constant temperature at 60°C for 20min, then add ethanolamine (1.0mL) to the solution, 60 The reaction was stirred at constant temperature for 20 minutes to obtain a transparent zinc sol, which was cooled to room temperature for later use. Add UiO-66-NH ₂ (0.0327g) to 1 mL of zinc sol, sonicate for 5 min, stir for 5 min, and cycle three times to make UiO-66-NH ₂ evenly dispersed in the zinc sol. After uniform dispersion, 2-methylimidazole (0.519g) was added to the sol and stirred rapidly for a few minutes to obtain a zinc gel containing UiO-66- _NH2 .

(3) Synthesis of UiO-66-NH ₂ mixed ZIF-8 matrix membrane: Spin-coat the zinc gel containing UiO-66-NH ₂ particles obtained in step (2) onto the AAO substrate, and dry at 120°C for 25 hours. After the reaction system is naturally cooled, the synthesized mixed metal framework film is taken out, soaked in the solvent methanol for 2 hours and dried in a methanol atmosphere for 24 hours to obtain the UiO-66-NH ₂ mixed ZIF-8 matrix film (Figure 1 is an SEM of Figure), the mass fraction of UiO-66-NH ₂ in ZIF-8 is 10 wt% (that is, the mass ratio of UiO-66-NH ₂ to ZIF-8 generated from zinc gel is 10%).

As shown in the XRD pattern in Figure 2 (where _UN ZM ₅ represents UiO-66-NH ₂ mixed ZIF-8 matrix film), the XRD pattern of the prepared UiO-66-NH ₂ mixed ZIF-8 matrix film is consistent with the The XRD patterns of the ZIF-8 membrane prepared in Example 1 are similar and the characteristic peaks of UiO-66-NH ₂ appear, indicating that the UiO-66-NH ₂ mixed ZIF-8 matrix membrane was successfully prepared under the experimental conditions. At the same time, the single-component gas separation performance of the UiO-66-NH ₂ mixed ZIF-8 matrix membrane was characterized by the constant pressure variable volume method. The experimental results are shown in Figure 3. Compared with the original ZIF-8 membrane of Comparative Example 1, The permeability of hydrogen, carbon dioxide, nitrogen, methane and propane of the UiO-66-NH ₂ mixed ZIF-8 matrix membrane increased significantly, and the permeation flux of hydrogen increased from 1925 Barrer to 3349 Barrer, indicating that the addition of metal organic framework particles can enhance the mixed metal Permeation flux of organic framework membranes. Moreover, the flux of each gas is different, and the UiO-66-NH ₂ mixed ZIF-8 matrix membrane shows good separation performance, indicating that the prepared UiO-66-NH ₂ mixed ZIF-8 matrix membrane is continuous and dense, and there are no obvious defects. .

Example 2

The MOF particles are MIL-101, the metal gel is zinc gel, the substrate is an anodized aluminum substrate (AAO), and the synthesized mixed metal-organic framework film is a MIL-101 mixed ZIF-8 matrix film.

Preparation:

(1) Preparation of MIL-101: Add chromium nitrate nonahydrate (1.2g), 1,4-phthalic acid (0.5g) and hydrofluoric acid solution (0.6mL) into deionized water (15.0mL) and stir 10 minutes. The mixture was transferred to a Teflon-lined stainless steel autoclave and heat treated at 220 °C for 8 h. After crystallization, the MIL-101 powder is separated by centrifugation and washed.

(2) Preparation of zinc gel containing MIL-101: Add zinc acetate (3.467g) to ethanol (10mL), stir at a constant temperature of 60°C for 20 minutes, then add ethanolamine (1.0mL) to the solution, and stir at a constant temperature of 60°C Stir the reaction for 20 minutes to obtain a transparent zinc sol without precipitation, and cool it to room temperature for later use. Add MIL-101 (0.0327g) to 1 mL of zinc sol, sonicate for 5 minutes, stir for 5 minutes, and cycle three times to make MIL-101 evenly dispersed in the zinc sol. After uniform dispersion, 2-methylimidazole (0.519g) was added and stirred rapidly for a few minutes to obtain a zinc gel containing MIL-101.

(3) Synthesis of MIL-101 mixed ZIF-8 matrix membrane: Spin-coat 200uL of the zinc gel containing MIL-101 particles obtained in step (2) onto the AAO substrate, dry at 120°C for 25 hours, and wait until the reaction system naturally After cooling, the synthesized membrane was taken out, soaked in the solvent methanol for 2 hours and dried in a methanol atmosphere for 24 hours to obtain the MIL-101 mixed ZIF-8 matrix membrane (Figure 4 is its SEM image), in which MIL-101 accounts for ZIF- The mass fraction of 8 is 10wt% (that is, the mass ratio of MIL-101 to ZIF-8 generated from zinc gel is 10%).

Example 3

The MOF particles are UiO-66, the metal gel is zinc gel, the substrate is an anodized aluminum substrate (AAO), and the synthesized metal-organic framework mixed metal-organic framework matrix film is UiO-66 mixed ZIF-8 matrix film.

Preparation:

(1) Preparation of UiO-66: Add zirconium chloride (0.53g) and terephthalic acid (0.3467g) to N,N-dimethylformamide (31.5mL) through stirring and sonication. The solution was transferred to a Teflon-lined stainless steel autoclave and heat treated at 120 °C for 24 h. After natural cooling, UiO-66 powder was separated and washed several times with N,N-dimethylformamide and methanol.

(2) Preparation of zinc gel containing UiO-66: Add zinc acetate (3.467g) to ethanol (10 mL), stir at a constant temperature of 60°C for 20 min, then add ethanolamine (1.0 mL), and stir at a constant temperature of 60°C for 20 min. , to obtain a transparent zinc sol without precipitation, and cool it to room temperature for later use. Add UiO-66 (0.1308g) to 1 mL of zinc sol, sonicate for 5 min, stir for 5 min, and cycle three times to make UiO-66 evenly dispersed in the zinc sol. After uniform dispersion, 2-methylimidazole (0.519g) was added and stirred rapidly for a few minutes to obtain a zinc gel containing UiO-66.

(3) Synthesis of UiO-66 mixed ZIF-8 matrix membrane: Spin-coat 200uL of the zinc gel containing UiO-66 particles obtained in step (2) onto the AAO substrate, dry at 120°C for 25 hours, and wait until the reaction system naturally After cooling, the synthesized membrane was taken out, soaked in the solvent methanol for 2 hours and dried in a methanol atmosphere for 24 hours to obtain the UiO-66 mixed ZIF-8 matrix membrane (Figure 5 is its SEM image). The UiO-66 accounted for The mass fraction of ZIF-8 is 40wt%.

Example 4

The MOF particles are UiO-66-NH ₂ , the metal gel is copper gel, the substrate is an anodized aluminum substrate (AAO), and the metal-organic framework mixed metal-organic framework matrix film is UiO-66-NH ₂ mixed CuBTC matrix film.

Preparation:

(1) Preparation of UiO-66-NH ₂ : UiO-66-NH ₂ is prepared by solvothermal synthesis method. Zirconium chloride (0.48 g) and 2-aminoterephthalic acid (0.372 g) were dissolved in N,N-dimethylformamide (40 mL) and water (0.19 mL) by stirring and sonication. The solution was transferred to a Teflon-lined stainless steel autoclave and heat treated at 120 °C for 24 h. After natural cooling, the powder was separated by centrifugation at 6000 rpm for 5 min. Finally, the obtained powder was washed several times with N,N-dimethylformamide and methanol.

(2) Preparation of copper gel containing UiO-66- _NH2 : Add copper nitrate trihydrate (3.817g) to ethylene glycol methyl ether (50mL), stir at 50°C for 40min, and then add ammonia water (1mL) , stir and react at 50°C for 20 minutes to obtain copper sol, which is left at room temperature for later use. Add UiO-66-NH ₂ (0.0327g) to 1 mL of copper sol, sonicate for 5 min, stir for 5 min, and cycle three times to make UiO-66-NH ₂ evenly dispersed in the copper sol. After uniform dispersion, trimesic acid (0.42g) was added and stirred rapidly for several minutes to obtain a copper gel containing UiO-66- _NH2 .

(3) Synthesis of UiO-66-NH ₂ mixed CuBTC matrix film: Spin-coat 200uL of the copper gel containing UiO-66-NH ₂ particles obtained in step (2) onto the AAO substrate, and dry at 120°C for 25 hours. After the reaction system is naturally cooled, the synthesized membrane is taken out, soaked in the solvent methanol for 2 hours and dried in a methanol atmosphere for 24 hours to obtain the UiO-66-NH ₂ mixed CuBTC matrix membrane. The UiO-66-NH ₂ accounts for The mass fraction of CuBTC is 10wt%.

Example 5

The MOF particles are UiO-66-NH ₂ , the metal gel is zinc gel, the substrate is polyethersulfone hollow fiber membrane, and the synthesized metal-organic framework mixed metal-organic framework matrix membrane is UiO-66-NH ₂ mixed ZIF-67 matrix membrane.

Preparation:

(1) Preparation of UiO-66-NH ₂ : UiO-66-NH ₂ is prepared by solvothermal synthesis method. Zirconium chloride (0.48 g) and 2-aminoterephthalic acid (0.372 g) were dissolved in N,N-dimethylformamide (40 mL) and water (0.19 mL) by stirring and sonication. The solution was transferred to a Teflon-lined stainless steel autoclave and heat treated at 120 °C for 24 h. After natural cooling, the powder was separated by centrifugation at 6000 rpm for 5 min. Finally, the obtained powder was washed several times with N,N-dimethylformamide and methanol.

(2) Prepare gel containing UiO-66- _NH2 : Add zinc acetate (3.467g) to ethanol (10mL), stir at constant temperature at 60°C for 20min, then add ethanolamine (1.0mL) to the solution, 60 The reaction was stirred at constant temperature for 20 minutes to obtain a transparent zinc sol, which was cooled to room temperature for later use. Add UiO-66-NH ₂ (0.0327g) to 1 mL of zinc sol, sonicate for 5 min, stir for 5 min, and cycle three times to make UiO-66-NH ₂ evenly dispersed in the zinc sol. After uniform dispersion, 2-methylimidazole (0.519g) was added to the sol and stirred rapidly for a few minutes to obtain a zinc gel containing UiO-66- _NH2 .

(3) Synthesis of UiO-66-NH ₂ mixed ZIF-8 matrix membrane: Take a 1cm long polyethersulfone hollow fiber membrane and soak it in the zinc gel containing UiO-66-NH ₂ particles obtained in step (2) for 1 min. Then take it out. Dry at 120°C for 25h. After the reaction system is naturally cooled, take out the synthesized membrane, soak it in the solvent methanol for 2h and dry it in a methanol atmosphere for 24h to obtain the UiO-66-NH ₂ mixed ZIF-8 matrix membrane. The mass fraction of UiO-66-NH ₂ in ZIF-8 is 10wt%.

Example 6

The MOF particles are UiO-66-NH ₂ and MIL-101, the metal gel is zinc gel, the substrate is an anodized aluminum substrate (AAO), and the synthesized metal-organic framework hybrid metal-organic framework matrix film is UiO-66-NH ₂ /MIL-101 mixed ZIF-8 matrix membrane.

Preparation:

(1) Preparation of UiO-66-NH ₂ : UiO-66-NH ₂ is prepared by solvothermal synthesis method. Zirconium chloride (0.48 g) and 2-aminoterephthalic acid (0.372 g) were dissolved in N,N-dimethylformamide (40 mL) and water (0.19 mL) by stirring and sonication. The solution was transferred to a Teflon-lined stainless steel autoclave and heat treated at 120 °C for 24 h. After natural cooling, the powder was separated by centrifugation at 6000 rpm for 5 min. Finally, the obtained powder was washed several times with N,N-dimethylformamide and methanol.

(2) Preparation of MIL-101: Add chromium nitrate nonahydrate (1.2g), 1,4-phthalic acid (0.5g) and hydrofluoric acid solution (0.6mL) into deionized water (15.0mL) and stir 10 minutes. The mixture was transferred to a Teflon-lined stainless steel autoclave and heat treated at 220 °C for 8 h. After crystallization, the MIL-101 powder is separated by centrifugation and washed.

(3) Preparation of zinc gel containing UiO-66-NH ₂ and MIL-101: Add zinc acetate (3.467g) to ethanol (10mL), stir at constant temperature at 60°C for 30min, then add ethanolamine (1.0mL) , react with constant stirring at 60°C for 20 minutes to obtain a transparent zinc sol without precipitation, and cool it to room temperature for later use. Add UiO-66-NH ₂ (0.0164g) and MIL-101 (0.0164g) to 1mL zinc sol, sonicate for 5 minutes, stir for 5 minutes, and cycle three times to make UiO-66-NH ₂ and MIL-101 in the zinc sol. Disperse evenly. After uniform dispersion, 2-methylimidazole (0.519g) was added and stirred rapidly for a few minutes to obtain a zinc gel containing UiO-66- _NH2 and MIL-101.

(4) Synthesis of UiO-66-NH ₂ /MIL-101 mixed ZIF-8 matrix membrane: Take 200uL zinc gel containing UiO-66-NH ₂ and MIL-101 particles obtained in step (3) and spin-coat it on the AAO substrate on the membrane, dry it for 25 hours at 120°C. After the reaction system is naturally cooled, take out the synthesized membrane, soak it in the solvent methanol for 2 hours and dry it in a methanol atmosphere for 24 hours to obtain the UiO-66-NH ₂ /MIL-101 mixture. ZIF-8 matrix membrane, the mass fraction of UiO-66-NH ₂ /MIL-101 in ZIF-8 is 20wt%.

Comparative example (no MOF particles added, original ZIF-8 membrane)

The metal gel is zinc gel, the substrate is anodized aluminum oxide (AAO), and the synthesized metal-organic framework film is ZIF-8 film.

Preparation:

(1) Preparation of zinc gel: Add zinc acetate (3.467g) to ethanol (10 mL), stir at a constant temperature of 60°C for 20 min, then add ethanolamine (1.0 mL), and react with constant stirring at a constant temperature of 60°C for 20 min to obtain a transparent product without precipitation. Zinc sol, cool to room temperature and set aside. Add 2-methylimidazole (0.519g) to 1 mL of zinc sol and stir rapidly for several minutes to obtain zinc gel.

(2) Synthesize ZIF-8 membrane: Spin-coat 200uL of the zinc gel obtained in step (1) onto the AAO substrate, dry it at 120°C for 25 hours, wait until the reaction system cools to room temperature, take out the synthesized membrane and use the solvent methanol Soak for 2 hours and dry under methanol atmosphere for 24 hours to obtain the ZIF-8 membrane.

The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, etc. may be made without departing from the spirit and principles of the present invention. All simplifications should be equivalent substitutions, and are all included in the protection scope of the present invention.

Claims (14)

1. The synthesis method of the mixed metal organic framework film is characterized by comprising the following steps of:

(1) Preparing metal organic framework particles: adding metal salt A and organic ligand A into solvent A, mixing uniformly to obtain synthetic solution, carrying out solvothermal reaction on the synthetic solution, naturally cooling after the reaction is finished, washing and drying to obtain metal-organic framework particles;

(2) Preparing mixed metal gel: adding metal salt B into a solvent B, stirring and dispersing uniformly at 30-80 ℃, then adding a chelating agent, continuing to stir and react for 10-80 min at constant temperature to obtain metal sol, adding metal organic framework particles into the obtained metal sol, uniformly mixing, cooling to room temperature, adding an organic ligand B, and stirring uniformly to obtain mixed metal gel containing the metal organic framework particles;

(3) Synthesizing a mixed metal organic framework film: and (3) coating the mixed metal gel containing the metal-organic framework particles obtained in the step (2) on a substrate, then carrying out heat treatment at 60-250 ℃ for 12-48h, naturally cooling to room temperature, taking out the synthesized film, soaking the synthesized film in a solvent C, and drying to obtain the mixed metal-organic framework film.

2. The method for synthesizing a mixed metal organic framework film according to claim 1, characterized in that:

the metal element in the metal salt A in the step (1) is one of Zn, al, fe, cu, ti, cr, co, ni, mg, zr, nb, mo, mn, sm, gd; the metal salt A is nitrate, chloride, carbonate, sulfate or acetate of metal;

the organic ligand A in the step (1) is one of 2-imidazole formaldehyde, 2-methylimidazole, 4-bromoimidazole, imidazole, benzimidazole, terephthalic acid, trimesic acid, 2-amino terephthalic acid and 1, 4-phthalic acid;

the ratio of the amount of the metal salt A to the organic ligand A in step (1) is 1: 0.5-8;

the solvent A in the step (1) is one of a solvent D, a mixed solution of the solvent D and water and a mixed solution of hydrofluoric acid and water, wherein the solvent D is at least one of methanol, N-dimethylacetamide, N-diethylformamide, N-dimethylformamide, octanol and ethanol;

the solvothermal reaction in the step (1) is to heat treat the mixture for 6 to 72 hours at the temperature of 40 to 300 ℃ in a stainless steel autoclave lined with polytetrafluoroethylene.

3. The method for synthesizing a mixed metal organic framework film according to claim 2, characterized in that:

the ratio of the amount of the metal salt A to the organic ligand A in step (1) is 1: 1-2.

4. The method for synthesizing a mixed metal organic framework film according to claim 1, characterized in that:

the metal element in the metal salt B in the step (2) is one of Zn, al, fe, cu, ti, cr, co, ni, mg, zr, nb, mo, mn, sm, gd; the metal salt B is nitrate, chloride, carbonate, sulfate or acetate of metal;

the solvent B in the step (2) is a derivative of monohydric alcohol, dihydric alcohol and alcohols;

the chelating agent in the step (2) is one of ethanolamine, ethylenediamine, diethanolamine, triethanolamine, 2-aminoethanol, triethylamine, diethylenetriamine or ammonia water;

the organic ligand B in the step (2) is at least one of 2-imidazole formaldehyde, 2-methylimidazole, 4-bromoimidazole, imidazole, benzimidazole, terephthalic acid and trimesic acid.

5. The method for synthesizing a mixed metal organic framework film according to claim 4, characterized in that:

the solvent B in the step (2) is one of ethanol, propanol, butanol, ethylene glycol, propylene glycol, glycerol, ethylene glycol ethyl ether or ethylene glycol methyl ether;

the chelating agent in the step (2) is one of ethylenediamine, ethanolamine or ammonia water.

6. The method for synthesizing a mixed metal organic framework film according to claim 1, characterized in that:

the volume consumption of the solvent B in the step (2) is 0.5-50 mL/g based on the mass of the metal salt B;

the ratio of the amount of chelating agent to the amount of metal salt B material described in step (2) is 1: 0.5-8;

the ratio of the amounts of the substances of the metal salt B to the organic ligand B in step (2) is 1: 0.5-12.

7. The method for synthesizing a mixed metal organic framework film according to claim 6, characterized in that:

the volume consumption of the solvent B in the step (2) is 2-22 mL/g based on the mass of the metal salt B;

the ratio of the amount of chelating agent to the amount of metal salt B material described in step (2) is 1: 1-3;

the ratio of the amounts of the substances of the metal salt B to the organic ligand B in step (2) is 1: 1-5.

8. The method for synthesizing a mixed metal organic framework film according to claim 1, characterized in that:

the metal-organic framework particles in the step (2) are at least one of the metal-organic framework particles prepared in the step (1);

the dosage of the metal organic framework particles in the step (2) satisfies that the mass ratio of the metal organic framework particles to the metal gel generated metal organic framework particles is 0-50%, and is not 0.

9. The method for synthesizing a mixed metal organic framework film according to claim 8, characterized in that:

the dosage of the metal organic framework particles in the step (2) satisfies that the mass ratio of the metal organic framework particles to the metal gel generated metal organic framework particles is 0-20%, and is not 0.

10. The method for synthesizing a mixed metal organic framework film according to claim 1, characterized in that:

the substrate in the step (3) is in a flat plate type, a tubular type or a hollow fiber type;

the substrate in the step (3) is made of polypropylene, polyethylene, alumina, titanium dioxide, copper, polytetrafluoroethylene, polyimide, polyether ether ketone, polyvinylidene fluoride, polyacrylonitrile, polysulfone, polyether sulfone, cellulose or zinc.

11. The method for synthesizing a mixed metal organic framework film according to claim 10, characterized in that:

the substrate in the step (3) is made of polysulfone, polyethersulfone, anodized aluminum, polyvinylidene fluoride, polyetherimide or polyacrylonitrile.

12. The method for synthesizing a mixed metal organic framework film according to claim 1, characterized in that:

in the step (3), the solvent C is at least one of methanol, N-dimethylacetamide, N-diethylformamide, N-dimethylformamide, octanol and ethanol.

13. A mixed metal organic framework film prepared according to the method of any one of claims 1-12.

14. Use of the mixed metal organic framework membrane according to claim 13 for gas separation and purification.